Knee height, knee pain, and knee osteoarthritis: the Beijing Osteoarthritis Study

Few risk factors for knee osteoarthritis (OA) are appreciated, and the discordance between symptoms and the severity of structural disease has not been explained. Knee height contributes to moments around the knee. The longer the leg, the more torque is present. Although this would suggest that having long legs would be related to the occurrence of knee OA and pain, this issue has not been studied. Our aim was to explore the association between knee height, knee pain, and knee OA.

We recruited a random sample of Beijing residents ages 60 years and older. Subjects answered questions about joint symptoms, and radiographs of their knees were obtained. A knee joint with a Kellgren/Lawrence grade of >/=2 was defined as having radiographic OA. Patellofemoral OA was defined as being present when grade >/=1 osteophytes or grade >/=1 joint space narrowing was observed on skyline views of the patella or anterior femur. Subjects were considered to have symptomatic OA when both radiographic OA and self-reported pain were present in the same joint. Knee height was measured on the right leg using a sliding broad-blade caliper; the subject was seated, and the subject's feet were bare. We used logistic regression analyses to assess whether knee height was associated with prevalent radiographic and symptomatic OA. We then assessed whether knee height was associated with knee symptoms independently of structural change.

A total of 1,006 men (mean +/- SD age 68.4 +/- 6.4 years) and 1,500 women (mean +/- SD age 67.5 +/- 6.1 years) participated in this study. Higher knee height was associated with an increasing prevalence of both radiographic and symptomatic OA, especially among women. For radiographic OA, the magnitude of association was similar for the patellofemoral and tibiofemoral compartments. Among women with knee pain, higher knee height was associated with more severe knee pain (P = 0.0004 for the highest quartile versus the lowest quartile of knee height) independently of the severity of radiographic OA.

Knee height is associated with prevalent radiographic and symptomatic knee OA. It may also play an important role in knee symptoms. This study highlights the importance of mechanical forces in the determination of OA and knee symptoms.